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Tip: EAA webinar on RV building tips!

H

humptybump

Well Known Member
I just finished "attending" the EAA webinar on RV building tips presented by Wally Anderson. It had some great recommendations!

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Here are just a few:

  • add black coloring to the epoxy resin when glassing the canopy so it gives a clean black look from the inside
  • hang the engine on its mount on an engine stand to do much of the FWF work and leave it on the stand for at least a month so the "sag" settles before fitting the cowl
  • cover bare skin with baby powder before sanding fiberglas to reduce itching

At least one of these tips is buried in the forums but I'd never have found it before watching the webinar.

The recording of EAA webinars get posted within a day or two.
 
I was "there" for that one too. I thought the suggestion to pre-hang the engine was a good one.

I was rather surprised to hear Wally say that many builders are skipping the drilling or reaming and deburring steps, and just dimpling the factory punched holes. While I am pretty sure that would give you holes large enough for the rivets, I can always tell immediately when I get a hole that I missed reaming -- the male dimple die won't fit. I have two of them, and neither will fit in a factory punched hole. Unless I really misunderstood what he said, or unless he was referring only to the RV-14 kits or something.
 
DaleB said:
I was rather surprised to hear Wally say that many builders are skipping the drilling or reaming and deburring steps, and just dimpling the factory punched holes.
Click to expand...

Was he mentioning in a sense that some do but shouldn't, or that he recommended it? Hopefully not a recommendation....
 
It sounded to me like a recommendation, but I could have been mistaken. I had to take a phone call somewhere in there and may have mis-heard. Maybe someone else who listened in will remember better than I do.
 
Thin material only

I also heard this webinar. He was talking about working with thin sheet metal, 3/32 I think, that has the factory punched holes. Says when you dimple the factory hole, it opens up large enough for the rivet. Said it only works for this one size material and rivet.
In the questions and answer part at the end, someone mentioned vansairforce.com as a good source. He said that it's a good source of information, but Be careful because you can get mis information. Get off the computer and out to the shop and work on your project
Some good pointers. Never heard the baby powder before you sand fiberglass. Have to try that one.
 
I took Wally's Empennage class at the start of my build...best thing I did. On a Saturday you get the basics of Al metal working. Then Monday through Friday in 40 to 45 hours, you build your entire empennage, with Wally or an expert building with you. After one week it's done properly and you've learned proper techniques.
 
SoCal Flyer said:
I also heard this webinar. He was talking about working with thin sheet metal, 3/32 I think, that has the factory punched holes. Says when you dimple the factory hole, it opens up large enough for the rivet. Said it only works for this one size material and rivet.
.
Click to expand...

He was referring to 3/32 or -3 rivets, not 3/32" sheet.
 
SoCal Flyer said:
He was talking about working with thin sheet metal, 3/32 I think, that has the factory punched holes. Says when you dimple the factory hole, it opens up large enough for the rivet. Said it only works for this one size material and rivet.
Click to expand...

He is right. The hole enlarges when you dimple which will allow insertion of a 3/32 rivet.
The problem is, if you use the commonly available dimple dies that have a #40 pilot, the pilot will not fit into the factory punched hole (which is .093, or about the same as a #42 drill) if it hasn't been final drilled.
So the dimple die pilot gets forced through the hole, pre-stretching it by about .006" and then the hole gets further stretched while the dimple forms.
This is greatly increasing the risk for radial cracking around the holes. Adding to that is that without final drilling/reaming, the interior of the holes has the same surface condition as a shear edge of the skin, which raises the potential for cracking even higher.

The recommendation to dimple without final drilling is a bad one.
 
Question for rvbuilder2002

Thanks for correcting my post about the sheet metal size and rivet size
Newbie question... Dimple die factory punched hole, THEN final drill? Or drill then dimple die?
Thanks in advance
 
SoCal Flyer said:
Newbie question... Dimple die factory punched hole, THEN final drill? Or drill then dimple die?
Click to expand...
Drill, then deburr, then dimple. I have actually mostly stopped using a drill bit for drilling pre-punched holes to final size - I got a #40 chucking reamer. Seems to make a little cleaner hole, but it could very well be my "new tool" bias. :)
 
SoCal Flyer said:
Thanks for correcting my post about the sheet metal size and rivet size
Newbie question... Dimple die factory punched hole, THEN final drill? Or drill then dimple die?
Thanks in advance
Click to expand...

Final drill first. Then debur as needed. Thendimple.

As mentioned in my other post, if you attempt to dimple the raw as supplied holes, the pilot of the dimple die will not fit into the hole. You have to force it into the hole which enlarges the hole by stretching (not a good thing).

For kits prior to the RV-12 and 14, all prepunched holes should be final drilled before dimpling.
Some builders skip the final drill in assembly step and just do all the holes in the separate parts. I have no problem with that because all the holes are at least proper diam. when they get dimpled. I don't think it saves a lot of time because you then have to separately drill a lot of holes that would have gotten drill in groups of 2 or 3 if parts were clecoed together, and it does risk the occasional possible hole alignment issue that would have been resolved with match drilling.
Builders prerogative....
 
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DaleB said:
I have actually mostly stopped using a drill bit for drilling pre-punched holes to final size - I got a #40 chucking reamer. Seems to make a little cleaner hole, but it could very well be my "new tool" bias. :)
Click to expand...

The drill bit makes a totally acceptable hole so that is why it is specified, but
a reamer is a good option and does make a nicer hole.
We have some in our shop that we use quite a bit.
Once again, builders choice... if you don't want to buy reamers, the drill bits are totally acceptable.
 
SoCal Flyer said:
Says when you dimple the factory hole, it opens up large enough for the rivet. Said it only works for this one size material and rivet.
In the questions and answer part at the end, someone mentioned vansairforce.com as a good source. He said that it's a good source of information, but Be careful because you can get mis information.
Click to expand...

Apparently the same is true of EAA webinars ;)
 
Back to Post #!

Does anyone know where you get the black coloring that Wally referred to for the epoxy resin when glassing the canopy?
 
Here is a test of the additives and strengths with various dyes/additives.

http://www.westsystem.com/ss/adding-pigments-to-epoxy/

I purchased 423-graphite powder for this purpose, but there is also 501.

The article is quite thorough and is downloadable for future reference. I think more research is needed on paint adherence to the 423 additive, but its adhesion is very good. Although I have not used it yet, my finding was, it made a pretty dense black mixture.

Good luck and if anyone has negative experience with 423 additive please sound off.
 
For kits prior to the RV-12 and 14, all prepunched holes should be final drilled before dimpling.


What is specifically diferent in the 12 and 14 kits?
 
Followed SOP but don't like it

I am certainly no expert but I have often noticed that my drilled-then-dimpled holes allow the rivet to wallow just a bit. Also, the nature of the process creates a cone-shaped hole when viewed from the convex side of the dimple.

If there was a suitably under-sized dimple die available, that would fit in an in-reamed factory pre-drilled hole, I think I would prefer to use that and then final-drill the entire stack of parts in assembly to get a perfectly clean cylindrical hole extending from the bottom of the dimple all the way to the shop head.

It is a bit late for me: my airframe is complete, but I still wonder are such under-sized dies available and if anybody had ever tested a method like that.
 
Loman said:
If there was a suitably under-sized dimple die available, that would fit in an in-reamed factory pre-drilled hole, I think I would prefer to use that and then final-drill the entire stack of parts in assembly to get a perfectly clean cylindrical hole extending from the bottom of the dimple all the way to the shop head.
Click to expand...

I have never research the specifics as to why, but I am pretty sure there are aircraft standards guides and documents that say enlarging/final drilling an already dimpled hole is not allowed.
 
A paper I remember reading said dimpled holes should not be reamed after dimpling because the dimpling process causes the holes to go a little off axis creating little ridges that the rivet fills and grabs creating a tighter rivet to hole fit.
Bill
 
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In this webinar Wally suggests putting the engine on the mount and bolting that to a piece of plywood which is in turn bolted to an automotive engine stand. That would put a lot of load on the plywood with the engine hanging way out there. Does anyone have any idea what thickness of ply is required?
 
rvbuilder2002 said:
I have never research the specifics as to why, but I am pretty sure there are aircraft standards guides and documents that say enlarging/final drilling an already dimpled hole is not allowed.
Click to expand...

Not really... if you are inserting a CherryMax rivet their documentation calls for parallel sides in the hole.

This is only possible if you drill/dimple undersize and enlarge the hole, mainly because the CherryMax rivets don't expand sideways the same as a driven rivet.

Enlarging/final drilling an already dimpled hole is specifically allowed.

Page 12 here describes exactly that process -

http://www.cherryaerospace.com/files/pdf/catalog/CA-1015.pdf
 
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Hi Scott,
I'm up to this stage and think I will go with 3/4" form ply. Will have to upgrade to longer bolts. Did Wally say to use all the bolt holes or only the corner. I'm assuming this is to give the mount time to settle with the weight from the engine. I can leave mine a bit longer.
 
I heard from Wally via email today and he uses 1 1/4" ply and a piece of steel angle across the top that ties together the upper 2 bolt holes. I would not want my brand new engine falling down so I will make sure mine is at least that strong. Probably if you had wood that thick the corner bolts would be enough.
 
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